This paper describes the preliminary results of an ongoing study to characterize the nature and sources of sub-micron aerosols in the Phillips Laboratory small scale supersonic COIL device. Heterogeneously nucleated aerosols from both sub- and supersonic flow regimes were sampled and characterized using the University of Missouri-Rolla, Mobile Aerosol Sampling System (MASS). Under all operating conditions where the oxygen generator discs were rotating, significant concentrations of aerosols were detected. Typically these aerosols had peak dry diameters of < 0.05 micrometers and nascent wet diameters of < 0.08 micrometers . Their total number density increased with increasing rotating disc velocity and with the addition of chlorine. A maximum number density of < 3000/cc was observed at maximum chloride flow rates when the initial generator mixture had been heavily depleted (i.e. neutralized with chlorine). The chemical compositions of these aerosols were found to be exclusively solution droplets of KOH and KCl. The critical supersaturation spectra for a KOH, KCl, I2 have been measured and compared to theoretical calculations thus permitting growth calculations based on laser operating conditions. Experiments to simulate, in a pure gas phase supersonic nozzle facility, cavity pressure increases indicative of homogeneous nucleation of aerosols were successful. Experiments to directly detect the presence of homogeneously nucleated aerosol under these clean simulation conditions are planned for the next phase of this program.